A VES is a spontaneous depolarization of the ventricle that is not properly triggered by a preceding atrial event and is out of the person's spontaneous or paced heart rhythm.
For persons having a cardiac pacemaker, in the event of detection of a VES, it is desirable to avoid the occurrence of pacemaker mediated tachycardia ("PMT"). PMT occurs when a VES induces a depolarization of the atrium which is sensed by the pacemaker and which, in turn, initiates an established atrioventricular delay interval and induces a stimulation of the ventricle after that interval. This can cause the pacemaker to accelerate improperly the pacing rate.